1. Field of the Invention
The following invention relates generally to flame detectors, and specifically to automated and programmable flame detectors.
2. Related Art
Boilers are used commercially to provide power for various commercial facilities. The commercial facilities can include anything from an office building, to larger facilities, such as power plants and paper mills.
A typical boiler will draw in hot water, boil it, and generate steam. The steam can be used, for example, to generate electrical power by pushing a steam turbine. The boiler, itself, is powered by a burner or burners. The burner is a device that combusts fuels, such as oil, gas, or coal.
In commercial facilities, particularly larger boilers, there are many burners operating side by side, up and bottom, and corner to corner to combust the fuels. Some boilers can have up to 64 burners operating at the same time. More complex facilities have a Burner Management System (BMS), which includes a safety system to prevent hazard, as well as a control system, to accurately control the temperature of the boiler. Depending upon the "loading conditions," which refers to the usage requirements, it is possible to turn on the burners selectively. For lower loading, most burners may be kept off, whereas for higher loading, it is possible to turn most or all burners on. The desired state is for the control system to keep on only the exact number of burners required for a particular loading condition, to maintain usage efficiency and to prevent hazard.
It is important to know if a burner is on or off at any given time to maintain proper control of the fuel supply to this burner for the whole boiler. For example, it is important to determine if a burner has been properly shut off. Direct observation is not likely convenient, and is likely inefficient or altogether impossible for multiple burners in one boiler. The burners operate at very high temperatures, making direct observation difficult. The fact that there are numerous burners, operating side by side, makes this task impossible. Moreover, in an automated system (for example, a modem burner management system), it is preferable to have the on/off conditions of the burners measured automatically, without human intervention, to save time and expense, and add other efficiencies. For this reason, commercial burners have flame detector devices to determine burner on/off conditions automatically.
The control system for most conventional flame detector devices use electrical circuitry to determine whether the burner flame is on or off based on pulse per second (PPS) measurement. An electrical circuit with an RC time constant (where R is resistance, and C is capacitance) is observed for a charge/discharge of capacitance, to produce PPS. Based on the PPS it is determined whether the flame is on or off. Unfortunately, these devices do not perform as well as desired, because they have slow associated operational timing, and limited accuracy, that means sometimes they report wrong flame conditions.
One type microprocessor/microcontroller based of flame detector device includes a photosensor device located near the targeted burner to detect the wavelengths of radiation emitted from the combustion and convert it to be an electrical signal. The signal is fed by a fiber optic cable to a receiving device. An amplifier in the receiving device amplifies the signal, and feeds it to a microprocessor/microcontroller device, which must determine from the detected radiation whether the burner is on or off. Each burner may have its own photodetector device, including a photosensor device and associated detection components.
Unfortunately, since a number of burners must operate side by side, it is often difficult to detect whether a particular burner is on or off. The reason is that the adjacent burners add background signal (or called background "noise") to the wavelengths of radiation detected from a particular burner (target burner). This background signal can cause a burner to be detected as being on, whereas it is actually off, or vice versa. The problem is particularly perplexing because several burners can contribute background signal to the target burner, and also because adjacent burners may burn different types of fuel to make background signal more complex.
There are also additional types of noises referred to as Gaussian noises, which make burner on/off condition detection difficult. Noise contributors taking a Gaussian distribution include noises caused by electrical devices in the environment and the temperatures of devices in the associated environment. Gaussian noises are wide band noises sometimes called white noise, which means they occur over the range of electromagnetic frequencies, and are not isolated to particular frequency ranges. This makes their removal difficult through conventional filters, because it is not possible to remove them with low pass, band pass, or high pass analog, even digital filters.
What is needed is a flame detector that more accurately detects burner on/off conditions by removing the associated noises, including noises from adjacent burners as well as background noises.